Method for in situ recovery of solid or semi-solid petroleum deposits



Dec. 19, 1967 .1. v. VOGEL 3,358,756

METHOD FOR 1N slTU RECOVERY OF SOLID OR SEMI-SOLID PETROLEUM DEPOSITSFiled March 12, 1965 l? le f 2o E HEAT I f H HEATER ExcHANGER :HITQ IlISG i PRODUCT\ LINE SEPARATION HIS ATTORNEY United States Patent O3,358,756 .METHOD FR I-N SITU RECGVERY F SOLID 0R SEMI-SOLID PETROLEUMDEPOSITS John V. Vogel, Houston, Tex., assignor to Shell Oil Company,New York, N.Y., a corporation of Delaware Filed Mar. 12, 1965, Ser. No.439,169 3 Claims. (Cl. 166-7) ABSTRACT 0F THE DISCLOSURE This inventionrelates to the recovery of petroleum existing in a solid or semi-solidstate from underground deposits, and more particularly, to a method ofin situ recovery involving -a cracking operation for converting solid orsemi-solid petroleum deposits into useful and recoverable hydrocarbonproducts.

' Substantial petroleum deposits exist in solid or semi- -solid form andthese deposits, the so-called oil shale deposits, are the greatest oilreserves in the United States. These deposits were formed apparentlyfrom fresh water lakes in which organic matter, mostly of algal origin,collected with nely divided silt at the bottom of Y fresh water lakes.This organic matter subsequently dried, became compacted and wastransformed into a laminated, impermeable organic-bearing mineral matrixknown today as oil shale.

The existence of the petroleum in such a semi-solid vf orm is notconducive to economic recovery by .present day techniques but,` 'becauseof the extensiveness of these oilshale deposits they provide more thanan adequate incentive to develop means of recovering the oil therefrom.For example, -the Green River formation, located midway between Denverand Salt Lake City, extends f o ver some 16,500 square miles, averaging15 or more gallons of desirable shale oil per ton. This isv probably theworlds single largest known hydrocarbon deposit with estimatedreservesuof over 150,000,000,000 barrels.

"Presently, there are two broad approaches to the re- `cover-y of shaleoil from the organic-inorganic matrix lknown as oil shale. One is retortof mined Ashale and the other is in situ treatment of the shale. Mostsuccessful today of the two general types of processes is the treatement. of mined shale by retort processes. The diculty with such aprocess is that a 50,000 barrel per day plant requires that 84,000 tonsof raw, good grade, shale be :processed through the plant per day andthat 71,000 tonsk of inorganic residue be-disposed of daily. Thus, thematerials handling pro'blems in such a process is enormous.

Because the organic matter in oil shale exists largely .as an insolubleresidue, often referred to as kerogen, having a molecular Weight of 3000plus, it is dillcult to separate the organic matter from the inorganicmatter without some modification of the kerogen. Heat converts it into aliquid or vapor form. This is the reason that retort processes mentioned-above are more successful than other types. These retort processesinvolving mining the oil shale, transporting the shale to a suitableprocessing v point, crushing and grinding the shale to a particle sizepermitting effective heat treatment and thereafter heating the resultingparticles sufficiently to effect destructive distillation of the kerogenare not today economical.

lCC

Even though the potential recovery of shale oil may be as high as 50 to75 gallons per ton, material handling problems have caused industry tolook for other methods of recovering the oil products from oil shales.This has led to the second lbroad approach to the recovery of organicmatter which involves attempts to heat the oil shales in situ to recoverthe useful organic matter. These latter techniques are much akin to theretort process and, in fact, many use in situ retort processes eitherburning the organic matter in the shale or providing fuel within theformation to develop sui-licient heat to cause destructive distillationthereby converting it to either recoverable liquid or vapor products.

While the in situ combustion processes eliminate the costly operationsof mining, transportation and processing of the raw oil shale, thevirgin oil shale is very strong and impermeable in its natural occurringstate which adds other problems. It is difficult to establish in situcombustion and to maintain it once it has been initiated Another problemfaced with in situ oil shale combustions When this art is used is thatthe produced gases are highly contaminated with nitrogen which mayreduce their fuel val-ue almost to nothing. Another diculty with in situcombustions is the presence of both magnesium carbonate and calciumcarbonate which begin to calcine from about 1100 to about l500 F. via anendothermic reaction Which is also undesirable.

Since both of the general techniques discussed abovehave their ownunique problems, other approaches to the recovery of organic matter fromoil shale have been sought. The present invention has resulted fromefforts to find a better technique to recover the organic matter fromthe oil shale and avoid some of the serious drawbacks of theaforedescribed techniques.

Broadly, the invention involves a new method of recovering solid tosemi-solid organic matter from underground formations, such as oil shaledeposits, including the steps of penetrating the formation with at leastone injection well and at least one production well, fracturing theformation between said wells, injecting a non-oxidizing heated vaporthrough the injection well, and recovering eflluents from the productionwell which includes organic materials formed from the solid to semisolidorganic matter in the formation by a thermal cracking action.

This invention will be better understood by referring to the attacheddrawing showing an earthen formation, taken in cross-section, includingan underground oil shale deposit and also the necessary surfaceequipment for practicing themethod of the present invention.

Because the present invention is particularly applicable to recovery oforganic matter from oil shales, some of the characteristics of suchshales should be considered. Generally, the inorganic material of oilshales is a laminated marlstone intimately mixed with clay and lesserquantities of sediment, plus other mineral constituents. The organicmatter. in a semi-pure form (often referred to as kerogen) is a brownamorphous powder having a molecular weight of 3000 plus. Because of thishigh molecular weight, kerogen is insoluble in common petroleum solventsat ambient temperatures and structurally appears to be a molecularcomplex of saturated, basically non-benzenoid, condensed polycyclic ringsystems loosely interconnected through -alkyl side chains which mayinclude hetero atoms.

Because of this nature of oilshales, the only industrial successfulprocess to date is destructive pyrolysis of crushed oil shale attemperatures in the order of 900 F. and at ambient pressures. Inpyrolysis, about 66% of the organic matter is converted to a liquid oiland 9% is converted to light gases with the remaining 25% sticking tothe inorganic matrix as a carbon-rich residue.

The process of the instant invention is specifically adapted to avoidthe necessity of mining the oil shale and processing it in a retort asknown commercially successful processes would require. Instead theinstant invention uses a hot vapor circulated through a fracture betweentwo wells to transfer heat underground. Heat is carried away from thehot fracture and into the oil shale formation by conduction, aidedsomewhat by convection. When sufficient heat has been transferred toraise the oil shale to a sufcient temperature, the organic matterundergoes thermal cracking. The vapor pressure of the hot newly formedproducts causes them to expand and be forced out of the shale and intothe fracture, adjacent permeable zones and/or the producing well. Thisprocess is aided somewhat by a sweeping action of the hot vaporcirculated as the heat carrying medium.

By properly controlling temperatures and withdrawal rates, the degree ofcracking of the organic matter can be controlled so as to favorpoduction of gas or oil. Generally speaking, gas products are favored-by higher temperatures and/or long exposure of the organic matter tothe cracking temperatures.

It may be preferred, but is not essential that the hot vapor, or aportion thereof, be an organic material which, rwhile not miscible withthe insoluble kerogen, is miscible with the cracked products obtained bycirculating the hot vapor through the shale formation. Since thepyrolysis of the organic matter in the oil shale produces heavycornponents Iwhich can be very viscous when in contact with coolerportions of the underground system, the misci'bility of the hot vaporwith the liquid conversion products may tend to lessen their viscosityand allow them to drain more freely from the inorganic matrix into thefractures, adjacent permeable zones, and/or the producing well.

It is desirable that the vapor injected have good heat carrying capacityin the temperature range of 650 to l100 F. This eliminates superheatedsteam which is somewhat limited in its ability to carry heat and isnonmiscible with the oil products. Vaporous hydrocarbons, therefore, areespecially desirable for carrying out the process. Further, an advantageis gained by using vaporous hydrocarbons since such hydrocarbons can beobtained on location for the use in the process which elirninates therequirement for large volumes of fresh water which would be difficult tofind in the arid region where oil shales are common.

In the practice of this invention, it is desirable that lighthydrocarbons which are themselves resistant to thermal cracking, beemployed in the vaporous phase to recover the organic matter from theundergound oil shale deposits. Generally, suitable hydrocarbons aremethane, ethane, propane, butane, kerosene, naphtha, gasoline, benzene,and the like. Benzene, butane and propane combine a high heat carryingcapacity with good resistance to thermal crackin-g. Another suitablemixture of gases which is even more resistant to thermal cracking,although of somewhat lower heat carrying capacity, is the gas producedby the process itself as the 4kerogen undergoes .destructiondistillation (hereafter termed shale gas). Because of the good heatcarrying capacity of the hydrocarbons referred to above plus theirmiscibility with the liquid products formed from the thermal cracking,they are able to achieve better cracking efficiency and removal ofproducts than immiscible superheated steam. Because the use of steam,especially at the temperatures involved, can cause unwanted tectonicchanges to occur within the formation that are not likely to occur withthe vaporous hydrocarbons, steam is not suitable in the instantinvention.

Generally, it is desired that the vaporous hydrocarbons be injected intothe formation at temperatures in excess of 700 F. In fact, it is verydesirable to heat the hydrocarbon vapors to a temperature well above 700F. in order to maintain the temperature in the area of central owbetween the two spaced wells at a temperature of at 4 least 700 F.Generally, the upper limit to which the vaporous hydrocarbons can beraised is limited to that point at which they themselves undergo thermalcracking or suffer degradation and this will depend largely upon theparticular hydrocarbon employed in the process.

For a better understanding of the invention, reference is made to thesingle accompanying gure showing an earthen formation in cross-sectionpenetrated by two spaced wells. The earthen formation 1 is composed of aplurality of strata and includes a reservoir formation 2 composedprincipally of oil shale. In practicing this invention, at least oneinjection well 3 and at least one production well 4 are drilled throughthe earthen formation to penetrate the shale formation Z. Theillustrated construction of both the injection well and the productionwell 3 and 4, respectively, is quite similar, each having a casing 5positioned in the borehole and sealed with a sealant `6 to maintain itslocation therein. Inside each casing string 5 is an insulated tubingstring 7 which is positioned in the casing string to leave insulatingannulus therebetween which is sealed near the lower end of the tubingstring 7 by packer 8.

Below packer 8, the casing string 5 is perforated in order to provideuid ingress and egress between the inside of the casing string 5 and theshale formation 2. It is generally preferred that the casing stringactually be severed in the area of the perforations since this portionof the casin-g string will be subjected to high temperatures and thisallows for expansion of the casing string.

Since, in all probability, the shale formation 2 will be impermeable, itwill be necessary to fracture between the input well 3 and theproduction well 4. Fracture 9 can be established by the use of hydraulicfracturing fluids and can be propped with propping agents 10 to insurethat it remains open during the injection of the hot hydrocarbon vapors.Not only may it be desirable to use propping agents 10, it may benecessary because of the expansion of the oil shale when heated whichwould tend to collapse the fracture if no propping agents are rpresent.

As it is desired that the hot hydrocarbon vapors be continuouslyrecycled through the formation to etect the recovery of the organicmatter therein, the discussion of the above ground equipment will beginwith the effluents of production well 4 and terminate with the injectionof the hot hydrocarbon vapors through injection well 3. At the wellhead11 of casing string 5 of the production well, the vaporous eiuents arerecovered through the insulated tubing string 7, pass through line 12and go .directly to heat exchanger 13 and thence into a separatingfacility 14 in which the cracked products from the formation areseparated from the hot hydrocarbon which was injected through theinjection well 3 to recover these products. Depending on the particularhydrocarbon mixture used, the separation facility 14 may consist ofsimple conventional equipment for separating gases and liquids bygravity or may require somewhat more elaborate distillation andcondensation equipment. The oil and gas products are recovered throughproduct recovery lines 15 and 15a and the heat carrying hydrocarbon,which was injected in vapor form, is removed from the separatingfacility 14 by line 16 and goes directly to heat exchanger 13 and thenthrough line 17 to pump or compressor 18. From pump or compressor 18,the hydrocarbon passes directly to a suitable heater 19 via line 20wherein the hydrocarbon is raised to a temperature in excess -of 700 F.

From heater 19, the heated hydrocarbon vapors are routed via insulatedpipe 21 to the wellhead 22 of the injection well 3. There the hotvaporous hydrocarbon travels down the insulated tubing string '7 ofinjection well 3 and proceeds via the tubing string and perforations 23to fracture 9. From the perforations 23 in casing string 5 of the lowerportion of injection well 3, the hot hydrocarbons enter fracture 9 andtransmit their heat by conduction and/or convection to the oil shaleformation adjacent to the fracture. As these hot hydrocarbon vapors owthrough the fracture 9 to the production Well 4, some of the organicmatter in the oil shale formation is thermally cracked to lower boilingproducts which are much less viscous. Once the cracked products from theorganic matter in the formation are reduced to low viscosity productsand/'or vaporized, they are forced out of their original position byexpanding vapor pressure and swept along lwith the hot hydrocarbon tothe production well from whence they are recovered via tubing string 7.As the circulation continues, the area of the shale formation 2 adjacentt-o fracture 9 will become depleted of much of the organic matter asindicated by the depleted zone 24. As the areas adjacent to fracturebecome depleted organic matter, it will become permeable to the hothydrocarbon vapors allowing them to contact more virgin shale.

In the instant process, since the circulation of the hydrocarbon occursin a closed circulatory system, little if any oxygen is available foractual in situ combustion which would occur at the temperatures in theformation if oxygen were present. Further, even if some oxygen isavailable within the formation, it is of little or no moment, since anextremely limited amount will be available to support combustion. Actualcombustion in the formation is not desired since it could adverselyaffect permeability.

Though we have discussed the invention relative to the use of two spacedwells, one of which is the injection well and one of which is theproduction well, it should be appreciated that it would be possible tocarry out the instant process in a single Well with dual insulatedtubing strings and through a vertical fracture.

Further, it should be appreciated that the facilities located above theground would all involve appropriate insulation in order to conservethermal energy and the use of appropriate heat exchangers in order torecover the maximum amount of thermal energy from the eluents from theproduction well. In this way, the efficiency of the process can beimproved and it can be operated on a commercial scale.

As the circulation of the hot hydrocarbons continues through the oilshale formation 2, the depleted zone 24 continues to expand as more andmore of the organic matter is stripped therefrom. In some cases, it maybe desirable to establish a fracture 9 at multiple levels in order tooptimize the effects of this process in the formation and to allow forirregularities in the formation itself. When the fractures are employedat multiple levels, the hot hydrocarbons can be injected into thefractures separately or simultaneously but usually separately in orderto avoid failure of the casing string resulting from a large segmentthereof being exposed to the relatively high temperatures. To avoidsimultaneous injections or exposing large areas of the casing to hightemperatures, a lower packer 25 may be used in each casing 5.

In order that the invention can be better understood, the followingexample is illustrative of the instant invention and method of carryingit out.

Example I In a mathematical model, it was determined that 950 F. benzenevapors injected into a shale formation through an injection well andrecovered at a production Well at 650 F. would give 55,000 B.t.u.s/bbl.to the formation. Calculated on four acre spacing with wells 300 feetapart and having liuid communication therebetween through the oil shale,an injection of 3260 barrels per day of 950 F. benzene vapors intofractures between the Wells will raise the temperature of a portion ofthe shale formation 25 feet on each side of the fracture to 750 F.within four years. The pressure drop will be 200l p.s.i. between thewells. If the shale has a richness of 30 gallons/ton of virgin oilshale, 442,000 bbls. of oil (or vaporous hydrocarbon equivalent) wouldbe given out of the four acre- 50 foot interval during the four yearperiod. An average of 300 bbls./day for the producing wells for theperiod.

The foregoing example is based on calculations and is not intended tolimit the invention. Various changes in injection rates and temperatureswill probably be necessary depending on the particular shale formationsand the gaseous eiiluents (shale gas) recovered from the formation willprobably be the most economical vapor to use in the instant process.

I claim as my invention:

-1. A method of recovering solid to semi-solid hydrocarbons from uniformunderground oil shale reservoirs comprising the steps of:

(a) pentrating such a reservoir with at least one in- -jection well andat least one production well;

(b) horizontally fracturing and establishing iluid communicationchannels through said reservoir between said injection well and saidproduction well;

(c) passing hot benzene through said reservoir by injecting it throughsaid fractured injecting Well into said uid communication channels at atemperature in excess of 650 F. to convert solid to semi-solidhydrocarbon residues in said formation to mobile fluids;

(d) recovering said mobile uids from said production Well; and

(e) separating said mobile iiuids into liquid and gaseous hydrocarbonfractions.

2. A method according to claim 1 in which a conventional propping agentis added to the fractures.

3. A method according to claim 1 in which the ilow rate through thereservoir and the temperature of the hot benzene is controlled so thatthe solid to semi-solid hydrocarbons are substantially converted tohydrocarbon vapor and which are recovered above ground, condensed andfractionated into liquid hydrocarbon oil and hydrocarbon gases.

References Cited UNITED STATES PATENTS 895,612 8/1908 Baker 166-571,422,204 7/ 1922 Hoover et al. 166-11 2,813,583` 11/1957 Marx et al.166-11 2,974,937 3/1961 Kiel 166--11 X 3,145,772 8/1964 Huitt 166-7 X3,241,611 3/1966 Dougan 166-11 X 3,284,281 11/1966 Thomas 166--11 XSTEPHEN J. NOV OSAD, Primary Examiner.

1. A METHOD OF RECOVERING SOLID TO SEMI-SOLID HYDROCARBONS FROM UNIFORMUNDERGROUND OIL SHALE RESERVIORS COMPRISING THE STEPS OF: (A)PENETRATING SUCH A RESERVOIR WITH AT LEAST ONE INJECTION WELL AND ATLEAST ONE PRODUCTION WELL; (B) HORIZONTALLY FRACTURING AND ESTABLISHINGFLUID COMMUNICATION CHANNELS THROUGH SAID RESERVOIR BETWEEN SAIDINJECTION WEL AND SAID PRODUCTION WELL; (C) PASSING HOT BENZENE THROUGHSAID RESERVOIR BY INJECTING IT THROUGH SAID FRACTURED INJECTING WELLINTO